/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkPositionIndex;

import com.google.common.annotations.GwtCompatible;
import java.util.ListIterator;
import java.util.NoSuchElementException;

/**
 * This class provides a skeletal implementation of the {@link ListIterator} interface across a
 * fixed number of elements that may be retrieved by position. It does not support {@link #remove},
 * {@link #set}, or {@link #add}.
 *
 * @author Jared Levy
 */
@GwtCompatible
abstract class AbstractIndexedListIterator<E> extends UnmodifiableListIterator<E> {
    private final int size;
    private int position;

    /**
     * Returns the element with the specified index. This method is called by {@link #next()}.
     */
    protected abstract E get(int index);

    /**
     * Constructs an iterator across a sequence of the given size whose initial position is 0. That
     * is, the first call to {@link #next()} will return the first element (or throw
     * {@link NoSuchElementException} if {@code size} is zero).
     *
     * @throws IllegalArgumentException if {@code size} is negative
     */
    protected AbstractIndexedListIterator(int size) {
        this(size, 0);
    }

    /**
     * Constructs an iterator across a sequence of the given size with the given initial position.
     * That is, the first call to {@link #nextIndex()} will return {@code position}, and the first
     * call to {@link #next()} will return the element at that index, if available. Calls to
     * {@link #previous()} can retrieve the preceding {@code position} elements.
     *
     * @throws IndexOutOfBoundsException if {@code position} is negative or is greater than
     *         {@code size}
     * @throws IllegalArgumentException if {@code size} is negative
     */
    protected AbstractIndexedListIterator(int size, int position) {
        checkPositionIndex(position, size);
        this.size = size;
        this.position = position;
    }

    @Override
    public final boolean hasNext() {
        return position < size;
    }

    @Override
    public final E next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        return get(position++);
    }

    @Override
    public final int nextIndex() {
        return position;
    }

    @Override
    public final boolean hasPrevious() {
        return position > 0;
    }

    @Override
    public final E previous() {
        if (!hasPrevious()) {
            throw new NoSuchElementException();
        }
        return get(--position);
    }

    @Override
    public final int previousIndex() {
        return position - 1;
    }
}
